Pyrotechnic smoke composition

ABSTRACT

A pyrotechnic composition which contains black phosphorus as fuel and which can be advantageously used in particular as a pyrotechnic smoke composition.

The present invention concerns a pyrotechnic composition, in particular a pyrotechnic smoke composition.

In general the white and red modifications of phosphorus are used in ammunition for producing aerosols based on phosphoric acid droplets.

White or colourless phosphorus, CAS-No [12185-10-3], is a highly reactive modification which spontaneously ignites at ambient temperature. Hence processing of white colourless phosphorus must always be effected under anaerobic conditions.

Red phosphorus, CAS-No [7723-14-0], is an amorphous modification which can be produced by various procedures from white phosphorus. Red phosphorus is stable at ambient temperature, it only ignites with oxygen above 300° C. and in contrast to colourless phosphorus is non-poisonous. Because of those advantageous properties, red phosphorus is frequently used in pyrotechnic smoke compositions as fuel.

Thus it is known for example from DE 199 14 097 A1 to use red phosphorus as a fuel in a pyrotechnic infrared screening smoke composition. The red phosphorus acts as a phosphorus source for consecutive generation of the oxide, P₄O₁₀ and the phosphoric acid, H₃PO₄, upon hydratisation. In that situation the red phosphorus is substantially vaporised upon the reaction of the energetic components of the pyrotechnic composition and oxidizes with a luminous flames upon contact with atmospheric oxygen to produce P₄O₁₀, which in turn reacts with the moisture in the air to afford phosphoric acid, H₃PO₄. A serious disadvantage of red phosphorus in practice however lies in its slow transformation to white phosphorus and the concomitant formation of phosphanes as a consequence of hydrolytic disproportioning. The presence of very small amounts of the thermodynamically relatively unstable white phosphorus is also the reason for spontaneous ignition and explosion, of mixtures of red phosphorus with strong oxidizers such as for example chlorates and/or perchlorates.

Therefore the object of the present invention is to provide a phosphorus-based pyrotechnic composition which is safer to handle than state-of-the-art red phosphorus-based compositions.

According to the invention that object is attained by a pyrotechnic composition as set forth in claim 1.

The pyrotechnic composition of the invention is distinguished in that it contains black phosphorus as fuel. That pyrotechnic composition can advantageously be used as a pyrotechnic smoke composition.

Black phosphorus is a crystalline modification of phosphorus which represents the most stable modification at ambient temperature. Although designated by the same CAS-No as Red and Hittorf, phosphorus [7723-14-0], it is characterized by the following features:

-   -   distinct X-ray diffraction; and     -   layered structure from polycondensed six-memebered rings.

In particular black phosphorus only reacts with oxygen above 400° C. That higher ignition temperature facilitates handling of the material and the corresponding pyrotechnic composition and reduces unintentional ignition due to pressure, friction, impact or the like, for which reason black phosphorus can also be used as a constituent of pyrotechnic aerosol compositions in physically highly loaded ammunition such as for example artillery ammunition.

In contrast to red phosphorus no phosphane development is observed when using black phosphorus.

In addition black phosphorus is of a markedly higher density of about 2.69 g/cm³, in comparison with white and red phosphorus. That results in an increase in the volume-related yield in the case of pyrotechnic compositions, in other words, a greater payload in relation to the overall weight of an item of ammunition.

Black phosphorus is also a semiconductor. That property reduces the risk of electrostatic discharges or ignition in the manufacture of the pyrotechnic compositions and further reduces the risks when dealing with that material.

Like red phosphorus black phosphorus is also non-poisonous, in contrast to white phosphorus.

All in all black phosphorus has properties which afford a use which is particularly advantageous in terms of safety aspects in the production and handling of pyrotechnic compositions for smoke compositions and ammunition. 

1. A pyrotechnic composition characterised in that it contains black phosphorus as fuel.
 2. A pyrotechnic composition according to claim 1 characterised in that the pyrotechnic composition is a smoke composition. 